The present invention relates to electrophotographic devices, and in particular, to current driver circuits and methods of controlling current driver circuits in electrophotographic devices.
In electrophotography, an imaging system forms a latent image by exposing select portions of an electrostatically charged photoconductive surface to laser light. For example, the imaging system may sweep a laser beam across the photoconductive surface in a scan direction as the photoconductive surface advances in a process direction that is orthogonal to the scan direction. For each sweep of the beam, a corresponding laser is modulated to write a plurality of print elements (Pels). Essentially, the density of the electrostatic charge on the photoconductive surface is altered in areas exposed to the laser beam relative to those areas unexposed to the laser beam, thus forming a latent image on the photoconductive surface in a manner that corresponds with associated image data. The latent electrostatic image thus created is developed into a visible image by exposing the photoconductive surface to toner, which contains pigment components and thermoplastic components. When so exposed, the toner is attracted to the photoconductive surface in a manner that corresponds to the electrostatic density altered by the laser beam.
The toner pattern is subsequently transferred from the photoconductive surface to the surface of a print substrate, such as paper, which has been given an electrostatic charge opposite that of the toner. A fuser assembly then applies heat and pressure to the toned substrate before the substrate is discharged from the apparatus. The applied heat causes constituents including the thermoplastic components of the toner to flow into the interstices between the fibers of the medium and the applied pressure promotes settling of the toner constituents in these voids. The toner solidifies as it cools adhering the image to the substrate.
Due to inherent imprecision in the imaging system, the swept beam may have bow and/or skew in its scan path. Moreover, there may be nonlinearity in the spacing between adjacent Pels due to imprecision in the imaging system optics. To compensate for such scanning errors, it is known to subdivide each Pel into a plurality of slices, i.e., subPels. During printing operations, the imaging system attempts to compensate for scanning errors by selectively controlling the number of slices per Pel and/or selectively controlling for each Pel, which slices the laser beam is modulated ON and which slices the laser beam is modulated OFF. However, as scan rates increase, e.g., due to increased printed page rates, the time available to the imaging system to write each slice of each Pel decreases. This places a burden on the imaging system, including the video control functions, the data transmission paths, and the laser diode driver(s) to reliably produce the short video pulse Pel slices.